The health booster is a special item that can be obtained exclusively from dungeons. Health Boosters, like other items only come in one rarity, its rarity happens to be novice. Health Boosters restores health to units that are alive. This means that if a unit dies completely, health Booster will not bring them back. Health Boosters have a one time use, so it is crucial that you use them at the right time.
Health Boosters can only be used outside of battles. On the map screen there will be an icon on the right hand side above items (See Figure 1.1). Upon clicking on this picture a new window will open (See Figure 1.2). In this window you can see how many Health Boosters you have. In the picture shown the user has 28 health boosters, which is represented by a x28 next to the Health Booster icon. To use a Health Booster simply click on the icon. Upon clicking, a confirmation window will pop up. Click yes to use the health booster, or click no to cancel.
On the right in figure 1.3 you can see the health boost in action. If you see these hearts it means that you have used your health booster. All of your units health should be filled.